This invention pertains to the art of cathodic protection apparatus used in a metal storage tank adapted to retain vast quantities of a liquid therein and, more particularly, to a support structure for mounting the protection apparatus in the tank.
The invention is particularly applicable to a water storage tank and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other tank or metal container environments and applications subject to the corrosive effect of an ionic liquid.
Tanks designed to store large quantities of water or other liquids for domestic and commercial use are well known in the art. Both high level tanks and ground storage tanks have been used for years for municipal or commercial uses. Typically, the water or other liquid corrodes the interior of the metal tank due to localized, galvanic action with the interior of the tank. Past practices have applied various coating compositions to the inner face of the tank wall in an effort to limit the corrosive interaction between the water and tank walls. This necessarily requires that the tank be emptied of its contents in order to apply the corrosion protective layer. Unless the tank is newly built and yet to be filled, this undertaking can become quite expensive due to the downtime of the tank.
Yet another protective avenue for limiting the corrosive interaction between the water and tank has been to employ some type of cathodic protection. Briefly, anodes and reference cells are suspended in the water. A direct current is impressed on the anodes whereby cathodic protection is provided and the ionic, corrosive action of the water on the metal tank walls is inhibited.
A prior cathodic protection device is illustrated in U.S. Pat. No. 3,718,554, issued Feb. 27, 1973 to Jacobs, et al. According to the Jacobs, et al. patent, a support structure includes a buoyant, submerged means formed of a material that floats in the liquid. An anode means is mounted in direct contact with the buoyant support means and flexible tie lines extend from the bottom of the tank to restrain the upward vertical movement of the buoyant support means. In this manner, a totally submerged condition of the anode means is maintained in an effort to prevent ice accumulation and damage.
Yet another construction for limiting damage due to ice accumulation in the water is disclosed in U.S. Pat. No. 3,954,591, issued May 4, 1976 to Conkling. Anodes hang by flexible suspension means extending from the roof of a water tank such that the dead weight of the anodes retains them in the liquid portion of the water tank. As ice forms at the top of the water, and the water level and ice layer move downwardly, there is a downward tensile force exerted by the ice on the suspension means resulting from adhesion therewith. This downward force reduces the diameter of the flexible suspension means which, in turn, frees the suspension means from gripping relation with the ice. Thus, the anodes are retained in the liquid.
In the Jacobs, et al. type of structure, the buoyant support means continuously urges the anode structure to the water level surface. This arrangement, likewise, continuously stresses the tie lines. On the other hand, during an extremely low water level situation, such as occurs in the summer season, there is no means to prevent the anode in a Conkling type of structure from being uncovered. That is, the anode will not always remain beneath the water level.
Further, periodic freezing and thawing of the liquid tends to deteriorate and break the flexible supports used in other similar structures which limit movement of the anode means. Still another problem associated with some of the prior art constructions is the requirement that the protection apparatus be installed in an empty tank. This severely limits retrofitting of existing tank systems with the cathodic protection due to the prohibitive expense of completely draining the water tanks.
The subject invention is deemed to overcome the above noted objections and others in a manner which is simple, economical, and may be retrofitted to existing tank systems.